1. Field of the Invention
This invention relates to a light source unit and a device provided with the same in which light emitting diodes (hereinafter, abbreviated as LEDs) are used as light sources, and more specifically, to an illumination device and a liquid crystal display device provided with the same.
2. Description of the Related Art
In general, illumination devices using point light sources (for example, LEDs) as light sources and liquid crystal display devices using the illumination devices tend to be widely used. In the following, description is made mainly of the liquid crystal display device and the illumination device therefor, but this invention is not limited to the liquid crystal display device.
The liquid crystal display device normally includes a liquid crystal panel and an illumination device (backlight unit) on a rear surface side of the liquid crystal panel. The illumination device for the liquid crystal display device includes, as a light source, a light source unit including a plurality of LEDs arrayed in a line on a wired substrate, and a light guide unit including a light guide plate which propagates light from the LEDs while reflecting the same with inner surfaces thereof. In this context, the light guide unit includes a saw-toothed or prismatic reflecting surface provided on an exit surface of the light guide plate, and a reflective sheet provided on a rear surface of the light guide plate. With this structure, the light from the LEDs is efficiently guided to the liquid crystal panel provided in an upper portion of the light guide unit.
In consideration of long-term use of the liquid crystal display device, it is desired to employ a structure which allows a light source unit using LEDs as light sources to be replaced.
As the liquid crystal display device, there have been proposed various types of liquid crystal display devices. For example, Japanese Laid-Open Patent Application Publication (JP-A) No. 2007-128820 proposes a liquid crystal display device in which a circuit substrate implemented with LEDs is mounted as a light source unit onto an illumination device. In the liquid crystal display device disclosed in JP-A 2007-128820, the circuit substrate provided to the illumination device is sandwiched by a chassis and a back case, and the circuit substrate is fixed to the back case with a double-faced tape. Further, a partially-thinned reflective sheet is inserted into a part at which a light guide plate and the circuit substrate overlap each other. Still further, the chassis, the back case, and the circuit substrate are fixed to each other with double-faced tapes.
In this structure, the part of the reflective sheet is thinned correspondingly to the part at which the light guide plate and the substrate overlap each other. Thus, a shift amount in a thickness direction of centers of light emitting surfaces of the LEDs and a center of a light incident surface of the light guide plate with respect to each other is reduced. As a result, light incident efficiency is enhanced in comparison with that in a case of using a normal reflective sheet having a uniform thickness, and hence luminance is enhanced. However, the chassis, the back case, and the circuit substrate are fixed to each other with the double-faced tapes, and hence it is difficult to replace the light source unit including the LEDs. In other words, in JP-A 2007-128820, replacement of the light source unit is not totally taken into consideration.
Meanwhile, Japanese Laid-Open Patent Application Publication (JP-A) No. 2007-311327 proposes a liquid crystal display device in which a light source substrate can be inserted through an insertion-and-removal hole formed through side surfaces of an upper case and a lower case. Further, through-holes are formed through a surface opposite to an exit surface of the lower case. In this structure, in order to fit a light source substrate, the light source substrate is inserted from the insertion-and-removal hole, and then a substrate holding member is fitted in a manner of being inserted into the through-holes of the lower case. In this way, the light source substrate and a side surface portion of the lower case can be held in a state of being sandwiched by an elastic force of the substrate holding member.
Further, Japanese Laid-Open Patent Application Publication (JP-A) No. 2008-218039 proposes an illumination device, in other words, a backlight unit in which a substrate implemented with LED light sources can be easily replaced. Specifically, the illumination device disclosed in JP-A 2008-218039 includes the substrate implemented with the LED light sources, a case for fixing the substrate, a substrate insertion-and-removal hole for freely inserting and removing the substrate with respect to the case, and a stopper for fixing the substrate in the case. In other words, the case is provided with a substrate insertion hole for implementation of the LED light sources and a hole through which the stopper can be inserted, the substrate insertion hole being closed by inserting the stopper.
In this structure, the substrate is inserted into the case, and then the stopper is inserted, with the result that the LEDs on the substrate hook onto the stopper. In this way, the substrate is fixed in the case.
Japanese Laid-Open Patent Application Publication (JP-A) No. 2009-238727 discloses a light source unit and a liquid crystal display device, in which, as illustrated in FIG. 10, a wired substrate 90 implemented with LEDs 80 is fitted to an LED cover 100 having a U-shaped cross-section. In this structure, a light guide plate is sandwiched from above and below by the LED cover 100.
In this structure, the LED cover 100 sandwiches the light guide plate from above and below. Thus, the LEDs and the light incident surface of the light guide plate are positioned in the thickness direction with respect to each other. In addition, the LED cover 100 is not bonded to other members, which leads to an advantage that the light source unit can be easily replaced.
In this context, when the LEDs and the light guide plate shift from each other in the thickness direction, a center of a light incident surface of the light guide plate and light emitting surfaces of the LEDs shift from each other. Thus, light incident efficiency is deteriorated. In JP-A 2007-128820, in order to prevent the shifts, the light source unit is fixed to the substrate with the double-faced tapes and the like. However, when the light source unit is fixed with the double-faced tapes in this way, it is difficult to replace the light source unit.
Meanwhile, as disclosed in JP-A 2007-311327, when the substrate holding member is used for holding and fixing the light source substrate, the light source substrate is positioned with respect to the upper case. Thus, the light incident surface of the light guide plate and the light emitting surfaces of the LEDs largely deviate in position from each other.
Further, as disclosed in JP-A 2008-218039, when the stopper is used for holding and fixing the substrate, the substrate is positioned with respect to the case. Thus, the light incident surface of the light guide plate and the light emitting surfaces of the LEDs largely deviate in position from each other. In addition, use of the stopper for holding the substrate leads to disadvantages that insertion of the stopper into the backlight unit involves time and efforts and a manufacturing cost increases.
Still further, as disclosed in JP-A 2009-238727, when the LED cover is fitted (refer to FIG. 10), the LEDs and the light guide plate are positioned with respect to each other in the thickness direction, and the light source unit can be easily replaced. However, disadvantageously, it is necessary to provide the LED cover in addition to the wired substrate. In other words, in order to assemble the light source unit, two steps are required: implementing the LEDs on the wired substrate; and after that, fitting the LED cover to the wired substrate, which leads to deterioration of assembly workability and an increase in manufacturing cost.